1. Field of the Invention
The present invention relates to an energy storage device (a power storage device) and a manufacturing method thereof.
Note that the energy storage device indicates all elements and devices which have a function of storing energy.
2. Description of the Related Art
In recent years, energy storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air cells have been developed.
The electrode of an energy storage device is formed by forming an active material over a surface of a current collector. As the active material, a material which can store and release ions functioning as carriers, such as carbon or silicon, is used. Specifically, silicon or phosphorus-doped silicon has higher theoretical capacity than carbon; thus, it is preferable to use the material as an active material in terms of increased capacity of the energy storage device (e.g., Patent Document 1).